In a typical electrostatographic printing process, such as xerography, a photoreceptor is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoreceptor is exposed to a light image of an original document being reproduced. Exposure of the charged photoreceptor selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoreceptor corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoreceptor, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoreceptor. The toner powder image is then transferred from the photoreceptor to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet. After each transfer process, the toner remaining on the photoconductor is cleaned by a cleaning device.
One specific type of development apparatus currently used in high-quality xerography is known as a hybrid jumping development (HJD) system. In the HJD system, a layer of toner is laid down evenly on the surface of a "donor roll" which is disposed near the surface of the photoreceptor. Biases placed on the donor roll create two development fields, or potentials, across the gap between the donor roll and the photoreceptor. The action of these fields causes toner particles on the donor roll surface to form a "toner cloud" in the gap, and the toner in this cloud thus becomes available to attach to appropriately-charged image areas on the photoreceptor.
In any xerographic development system in which there is a substantial potential relative to the photoreceptor, but particularly when there exists an alternating current field across a development gap, there is a practical risk of arcing across the gap. Such arcing will of course have a deleterious effect on the operation of the printing apparatus, causing at the very least a print defect and at worst damage to the apparatus. The various control systems for maintaining print quality in any xerographic printing apparatus are liable to cause the various potentials associated with the xerographic process to reach such levels that arcing is possible. The risk of arcing is particularly increased in situations where the printing apparatus is installed at high altitudes, such as in mountainous regions. The relatively low air pressure in at higher altitudes can lead to Paschen breakdown, that is, the ionization of air molecules which leads to arcing, at much lower potentials than would occur at lower altitudes.
The present invention is directed toward a system in which conditions conducive to arcing are detected, and the control systems over the xerographic process are, if necessary, modified to avoid these conditions.